tarsnap-recrypt man page

tarsnap-recrypt downloads and decrypts data using old-key-file and re-encrypts and uploads it using new-key-file. After all the data has been re-uploaded, tarsnap-recrypt deletes the data using old-key-file so that the only remaining copy of the data is encrypted using new-key-file. The key file new-key-file must have been generated by tarsnap-keyregen(1) with old-key-file.

tarsnap-recrypt checkpoints its progress after every 1-2 GB of data that it has copied; if it is interrupted it can be re-run and it will attempt to continue.

Note that after tarsnap-recrypt completes it will be possible to store more archives using the key old-key-file and the cache directory old-cache-dir so care should be taken to disable any automatic (e.g., cron(8)) archiving while tarsnap-recrypt is run.